This subroutine reads the contents of a database file into hash and returns it.
FileName - The file you are trying to retrieve, including the full path.
These are actual examples from the Aneuch source code:
%F = ReadDB("$ArchiveDir/$ShortDir/$newrev");
In this example, which comes from the DoDiff sub, the database will be read in from $ArchiveDir/$ShortDir/$newrev, and the contents will be stored in the hash %F.